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Canadarm2's cosmic catches

Canada's contribution to the International Space Station (ISS) includes Canadarm2, the robotic arm that helped build the orbiting laboratory. The versatile Canadian invention is now used for regular maintenance tasks, and also lends a helping hand to "catch" unpiloted cargo ships.

What is a cosmic catch?

Unpiloted ships are launched from Earth to bring supplies to the Station. These ships contain cargo, or payloads, such as:

As these ships approach the ISS, astronauts on board use Canadarm2 to grapple the ships and berth them to the Station. This tricky manoeuvre is known as a cosmic catch.

Cargo vehicles

Unpiloted vehicles bring thousands of kilograms of cargo to the Space Station. The following three ships are caught by Canadarm2:

A fourth type, the Progress spacecraft, resupplies the Russian section of the Station without assistance from Canadarm2.

Animation of Canadarm2 catching and berthing SpaceX's Dragon. (Credit: Canadian Space Agency)

How a cosmic catch works

Catching an unpiloted cargo ship calls for extremely precise work from Canadarm2:

  1. Approach

    With the help of GPS technology and a laser navigation system, the cargo ship slowly approaches the Station. Once the ship is approximately 500 metres below them, the Space Station crew begins to monitor its progress to ensure a safe approach. The visiting ship then moves closer by occasionally firing its thrusters.

  2. Alignment

    The guidance and control system synchronizes the vehicle's movements with those of the Station. The two spacecraft fly in formation at an altitude of approximately 400 km above Earth and a speed of about 28,000 km/h.

  3. Catching and berthing

    An astronaut on board the ISS extends Canadarm2 and catches the ship. Once it has been caught, the crew collaborates with the ground team to berth it to one of the Station's ports.

  4. Unloading

    The astronauts then open the airlocks between the Station and the ship and unload the contents. Dextre can also help unload bigger, bulkier items from the "trunk" of some of these vehicles, especially the HTV. Cargo ships can remain docked to the ISS for up to a month.

  5. Return

    Once the mission is complete, the vehicle is released from the Station.

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